Sign up with Google is not permitted.

It is supposedly the latest version 7.1.0+build.2017.11.07.15.08.03.f3e405876 for cbconnect
CB is 2.1.3
I turned the debug on for google but did not see any different result. Where is the log?

CB is 2.1.3

That's a stable release. We've had several build releases since then. Please download and install latest CB build and retry. Beyond that I don't know what to suggest as this all works fine in my tests.

I turned the debug on for google but did not see any different result. Where is the log?

Joomla debug mode and maximum error reporting also need to be enabled for CB to stop its redirect and output the debug information.

The google hook seems to work only with registration turned on in a create new account mode. We can't have that. We can only link existing users. What are the settings for linking to existing users only? That seems to be our problem.

Registration shouldn't need to be turned on to allow login of existing linked users. Based off your post below it's trying to register a new account every time.

www.joomlapolis.com/forum/153-professional-member-support/238506-sign-up-with-google-is-not-permitted?limitstart=0#301729

Is that still the case? or are accounts created using the Google Sign Up button the only ones working correctly?

I have a similar problem but with facebook registration is fine, linking is also fine but when I try login I get the message. The email 'marlonmurahwa@gmail.com' is already in use. Please login to link your account.

Check the user created by CB Connect and ensure their provider field id has been supplied. If Facebook for example check that Facebook ID field has a value. Do not map core CB fields or the provider field in the Registration tab of various providers within CB Connect > Parameters.